The present disclosure describes power supply in aircraft but this is by way of example only and the principles of the disclosure could be applied to other power supply systems e.g. on ships or in large plants or the like.
Aircraft require electrical power to operate many parts of the aircraft system, including on-board flight control systems, lighting, air conditioning etc. The current and future generations of aircraft use more and more electrical control in place of convention hydraulic, pneumatic etc. control. Such MEA aircraft have advantages in terms of the size and weight of the controls and power systems as well as in terms of maintenance and reliability.
Most current large commercial aircraft use electricity, on-board, in the form of an AC fixed frequency and/or variable frequency network. Steps have been made to move from 115 V ac to 230 V ac and more recent developments have allowed power supplies to supply both ac and high voltage dc (HVDC) e.g. +/−270 V dc, providing improvements in terms of additional functionality, power supply simplification, weight savings and thus fuel efficiency.
Generally, voltage is provided on board aircraft in one of two (or more) ways. When the aircraft is on the ground, power comes from an external ground generator supplying, say 115 V ac at 400 Hz. An auto-transformer rectifier unit (ATRU) rectifies the supply voltage to provide voltages required for the different loads on the aircraft. Instead of an ATRU, the power can be rectified by active rectification using power flow controllers.
When the aircraft is in the air the power comes from the aircraft engine or aircraft power unit (APU) via a three-phase ac variable frequency generator VFG and power to the loads is provided via a simple 6-pulse rectifier.
U.S. Pat. No. 8,358,111 teaches a dual source electric power generating system that can provide both a regulated AC output and a regulated DC output.
The rectifier units in these known systems are complex and require the use of capacitors. Capacitors are, however, a common point of failure and can be responsible for 20% to 40% of power electronics failures. Also, the physics of capacitor charge storage mean that rapid or step-wise output regulation is difficult.
Based on the above, there is a need for improved power supply systems that overcome these problems.